1. Technical Field
The present invention relates to multicasts and, in particular, assignment of resources and modulation and coding schemes to layers of multicast data streams.
2. Description of the Related Art
Next generation cellular wireless networks, such as 4G, are expected to deliver a much higher spectrum efficiency and bandwidth than existing networks. The International Telecommunication Union (ITU) requires that 4G technology should provide peak data rate of 100 Mbps for high mobility applications and 1 Gbps for low mobility applications. Such a high bandwidth enables the provision of real-time video services, such as Internet Protocol Television (IPTV) services, live video streaming and online telecast of sports.
Nevertheless, due to the fact that the available wireless spectrum is typically shared by many users and that each streaming video service may have very large bandwidth and stringent delay requirements, efficient resource allocation is an important aspect in developing cellular wireless network technology.
Adaptive modulation and coding schemes are currently used in wireless networks to provide efficient resource allocation. Here, the transmitters, such as base stations providing video streaming services, can adaptively select the modulation and coding scheme (MCS) to be applied when transmitting data to receivers. In particular, the MCSs employed can be receiver-specific in that they are based on different channel qualities measured at a receiver and on different receiver device capabilities. However, in wireless multicast services, the receivers can have fading channel conditions, various instantaneous channel conditions due to their different respective distances from the base station, etc. Adaptive modulation and coding schemes enable the determination of which MCS should be used for a multicast frame. Normally, a robust modulation and coding scheme that is receivable by all wireless clients in the multicast group is typically employed to accommodate all receivers. As a result, the multicast data rate and video quality are limited by the users with the worst channel conditions.
To address this limitation in a wireless video multicast scenario, scalable video coding (SVC) schemes have been developed. Scalable video coding schemes divide a video stream into multiple sub-streams, denoted as layers. An SVC stream has one base layer and one or multiple enhancement layers. The base layer provides a minimum quality, frame rate and resolution of the video and the enhancement layers represent the same video at gradually increasing quality and/or frame rate and/or resolution. Therefore, by applying different MCSs on different layers of the scalable video sequence, essential video service can be provided to all the users via the base layer with a low rate MCS while the enhancement layers with a high rate MCS can help improve the video quality for the users having good channel conditions.
While scalable video coding provides flexibility and high performance, scalable video coding also presents great challenges in designing an efficient resource allocation scheme. Recently, a fast greedy resource allocation algorithm was developed for both single-session and multi-session video multicast services. This algorithm uses a utility function that is the logarithm of the received throughput to achieve user fairness. A strong assumption is made in this algorithm that all the enhancement layers have the same size, which limits its applicability in practice. Another approach generalizes the model with the support of flexible layer rates and a general utility function. An optimal pseudo-polynomial algorithm based on dynamic programming has been proposed for both single-session and multi-session scenarios.